This invention relates to a fuel injection control system for internal combustion engines. A fuel injector for internal combustion engines is well known which comprises a fuel injection valve having a servo-piston of a large diameter and a plunger of a small diameter and a fuel injection nozzle connected thereto, a pressure differential of the fuel introduced from a pressurized fuel supply source into said servo-piston and plunger acting to open and shut said fuel injection nozzle thereby enabling a high pressure fuel injection to be made.
Disclosed in the Japanese Pat. No. 51-18010 is a unit injector wherein the timing and amount of fuel injection etc. can be controlled by one solenoid-operated spool valve. This system is, however, disadvantageous in that since the metering of fuel is made during draining of the spool valve, the moving speed of the valve tends to become unstable, and consequently changes in the amount of metering are liable to occur.